Potential basis of glyphosate resistance in California rigid ryegrass (Lolium rigidum)

Abstract

Glyphosate-resistant rigid ryegrass has been identified in California, but research has yet to elucidate the resistance mechanism. The objectives of this study were to examine the differences between sensitive and resistant rigid ryegrass in absorption and distribution of glyphosate, in vivo and in vitro absorption by chloroplasts, and shikimic acid accumulation after glyphosate treatment. Foliar absorption and distribution of 14C-glyphosate did not differ 1 to 3 d after treatment (DAT) between the susceptible (S) and resistant (R) biotypes. Absorption of 14C-glyphosate by isolated chloroplasts also did not differ between the S and R biotypes. After foliar application of 14C-glyphosate, chloroplasts were isolated from treated leaves from both biotypes. Accumulation of 14C-glyphosate in the chloroplasts did not differ between the two biotypes. Shikimic acid level increased significantly in the S biotype after treatment with glyphosate at 2.24 kg ai ha−1 to levels 10-fold greater than in the R biotype 11 DAT. Shikimic acid in the germination media at 2 to 5 mM did not affect seed germination of S and R biotypes but drastically decreased the length of coleoptiles of both at 5 DAT. Thus, biotype differences in sensitivity or metabolism of shikimic acid do not explain differences in sensitivity to glyphosate.

Testing Methods for Glyphosate Resistance

“…Shikimate accumulated in both GS and GR horseweed populations from Tennessee by 2 DAT, but declined 40% in the GR populations between 2 and 4 DAT, while it increased 35% in the GS populations (Mueller et al 2003 ). Similar responses have been reported in GR biotypes of hairy fl eabane, rigid ryegrass, and Italian ryegrass (Dinelli et al 2008 ;Michitte et al 2007 ;Simarmata et al 2003 ;Wakelin and Preston 2006 ). Shikimate accumulated to similar levels in both GS and GR biotypes after treatment with glyphosate at 2 to 4 DAT, but the shikimate level decreased or remained the same in the GR biotypes; whereas, it continued to increase in the GS biotypes.…”

In Vivo 31P-Nuclear Magnetic Resonance Studies of Glyphosate Uptake, Vacuolar Sequestration, and Tonoplast Pump Activity in Glyphosate-Resistant Horseweed

“…Environmental factors affecting its uptake and translocation in higher plants have been widely studied (Kells and Rieck, 1979;Coupland, 1983;Devine et al, 1983;Masiunas and Weller, 1988;Zhou et al, 2007). Notably, the role of light is important for effective uptake and translocation, suggesting that metabolic energy plays a role in this process (Simarmata et al, 2003;Shaner et al, 2005). Death of the whole plant requires effective glyphosate translocation from source to sink tissue, a process requiring ATP to maintain Suc gradients, which drive phloem movement (Bromilow et al, 1990;Dill et al, 2010).…”

Resistência de Conyza canadensis e C. bonariensis ao herbicida glyphosate

“…Atualmente existem sete espécies de plantas daninhas com casos relatados de biótipos resistentes ao glyphosate: Eleusine indica, na Malásia (Tran et al, 1999;Lee & Ngim, 2000); Lolium rigidum , na Austrália e nos Estados Unidos (Powles et al, 1998;Pratley et al, 1999;Simarmata et al, 2003); Plantago lanceolata, na Áf ri ca do Su l (H ea p, 20 04 ); Co ny za bonar iensis , na Áf rica do Sul e Es pan ha (Urbano et al, 2005); Lolium multiflorum, no Brasil, Chile e nos Estados Unidos (Perez & Kogan, 2003;Christoffoleti et al, 2005;PerezJones et al, 2005); Conyza canadensis, nos Estados Unidos e na África do Sul (VanGessel, 2001;Koger et al, 2004;Main et al, 2004) (Heap, 2004).…”